This invention relates to an input device for use with a display device such as a cathode ray tube (CRT) as a computer terminal, and more particularly to a touch type input device wherein a position of a surface of a panel at which it is pressed by a touch pen or the like is detected.
Various systems have been proposed so far for this type of input devices, for example, an electrode contact type in which membrane switches are contained, a photo matrix type wherein a light source and a photosensor are used in combination such that a coordinate of an obstacle on a light path may be detected thereby, a pressure type wherein pressure by touch is detected, and a surface elastic wave type wherein a coordinate is detected by a propagation time of a surface wave along a panel surface. Among these types of systems, the electrode contact type is simpler in construction and is reduced in cost comparing with the remaining types. However, a coordinate input device of the conventional electrode contact type includes therein keyboard switches of a membrane type which employs a transparent plastic film which has evaporated or sputtered thereto a membrane of a metal material such as Ag, Pd and so on, or a membrane of a metal oxide such as In.sub.2 O.sub.3 and so on over a predetermined area. Accordingly, an input device of this type is disadvantageous in that it has a relatively high contact resistance and a rather low mechanical strength so that the available percentage becomes low and the life becomes short. Further, some membrane electrodes have fine powder of a conductive metal material dispersed in a synthetic resin material. But, dispersion of such metal powder is not always uniform, and hence, accurate detection of coordinates is sometimes obstacled and satisfactory strength cannot be attained.